Field
The invention relates to a coupling assembly for coupling a rod to a bone anchoring element. The coupling assembly includes a receiving part with a recess for receiving the rod and an accommodation space for accommodating a head of the bone anchoring element, a pressure element to clamp the head, and a separate rod receiving element that is connectable to the pressure element and configured to support the rod. The pressure element has at least one spring portion that extends over a length in a circumferential direction and that is configured to engage a portion of an inner wall of the receiving part so that the pressure element can be held in a position that prevents an inserted bone anchoring element from being removed. The invention further relates to a bottom loading type polyaxial bone anchoring device with such a coupling assembly. Still further, the invention relates to a modular polyaxial bone anchoring device including the coupling assembly and at least two different rod receiving elements that can be used interchangeably with at least two associated closure mechanisms. The invention further relates to a modular stabilization device using the polyaxial bone anchoring device and at least two stabilizations rods having different diameters or one rod with at least two sections having different diameters.
Description of Related Art
US 2010/0234902 A1 describes a receiving part for receiving a rod for coupling the rod to a bone anchoring element, the receiving part including a receiving part body with a channel for receiving the rod and defining an accommodation space for accommodating a head of a bone anchoring element and a pressure element at least partially provided in the accommodation space. In one embodiment the pressure element comprises two upstanding resilient fingers with outwardly directed portions at their free ends that can snap below pins extending through the wall of the receiving part in order to secure a pre-locking position of the pressure element in which the head can no longer be removed through the bottom end of the receiving part.
US 2010/0160980 A1 describes a locking mechanism and a method of fixation of a bone screw and a rod to the spine. The locking mechanism includes a body, an insert, a rod seat and a set screw. The body includes a bottom portion configured to receive the bone screw and the insert, but prevents the insert and the bone screw from passing therethrough once the insert and the bone screw are engaged. The rod seat is between the rod and the insert.